Method of and apparatus for coating paper



Aug. 21, 19 JQ J. O'CONNOR ETAL METHOD OF AND APPARATUS FOR COATING PAPER Original Filed Sept. 26, 1939 5 Sheets-Sheet l 1951 J. J. O'CONNOR ETAL 2,565,260

METHOD OF AND APPARATUS FOR COATING PAPER Original Filed Sept. 26, 1939 5 Sheets-Sheet 2 1951 J. J. OCONNOR ETAL 2,565,260

METHOD OF AND APPARATUS FOR COATING PAPER Original Filed Sept. 26, 1959 5 Sheets-Sheet 5 ,Aug. 21, 1951 J. J. O'CONNOR ETAL METHOD OF AND APPARATUS FOR COATING PAPER Original Filed Sept. 26, 1959 5 Sheets-Sheet 4 1951 J. J. O'CONNOR ET AL 2,565,260

METHOD OF AND APPARATUS FOR COATING PAPER Original Filed Sept. 26, 1939 5 Sheets-Sheet 5 Patented Aug. 21, 1951 METHOD OF AND APPARATUS FQR COATING PAPER James J. OConnor, Russell H. Savage, and Hellmuth .C. Schwalbe, Chillicothe, Ohio, assignors, by mesne assignments, to The Mead Corporation, Chillicothe, Ohio, a corporation of Ohio Continuation of application Serial No. 296,690, September 26, 1939. This application April 28, 1947, Serial N0. 744,294

(Cl. l17111) 14 Claims. 1

This invention relates to the manufacture of paper, and more particularly paper having suitable application of a finely divided finish imparting mineral to the surface thereof to provide a printing surface adaptable for high grade and exacting printing requirements, such as halftone and multiple color reproduction work in magazine illustrations and the like, and is adaptable for use in the manufacture of such paper as a continuous paper making operation.

One of the principal objects of the invention is to provide a new. process of producing such paper with a mineral finished surface of high degree of smoothness and finish adapting it for such .high grade multi-color reproduction and half-tone magazine illustration work, and with high speed operation to produce a product of quality equal to, or comparable with, that of mineral finished or coated paper as made by any other practiced process which is eilicient and eifective in operation and its controls.

Another object is to provide a process for producing a mineral suspension which may be effectively and efficiently applied to produce such a paper having said quality surface finish.

Another object is to provide a process of applyin such mineral material to paper to produce paper having such surface finish.

Another object of th invention is to provide novel apparatus for carrying such processes into effect to produce such products. r

Still another object of the inventon is to provide novel apparatus, adaptable for us in the manufacture of a book paper having a mineral finished surface of the characteristics described as a continuous paper making operation and applied under varying degrees of moisture content of the formed paper web, and providing for unusual effectiveness in the production of such paper.

Other objects and advantages of the invention will be apparent from the following description and claims and the drawing, when considered in connection each with the other.

In the drawing, in which like characters of reference designate lik parts throughout the several views thereof.

Fig. l is a diagrammatic view in side elevation of the first section of q, paper making machine constructed according to, and for carrying out, the preferred embodiment of the invention;

Fig. 1A is a corre ponding diagrammatic side elevational view of the remaining portion .of said machine, the line A-A, which appears at the right and the left ends of Figs. 1 and 1A respectively, indicating the line of division between these two portions of the continuous machine, for purposes of illustration herein;

Fig. 2 is an enlarged side elevational view of one of the units for applying the final surfacing mineral suspension to the paper web;

Fig. 3 is a view in elevation, with som parts in section and other parts omittedfor clearer illustration, at right angles to Fig.2, along the line 3-3 of Fig. 2 and looking in the direction of the arrows, and with parts omitted forclearer illustration; I

Fig. 4 is a detailed view of parts of the mechanisms of Fig. 2;

Fig. 5 is a corresponding detail view of the same mechanisms, shown at right angles to Fig. 4; Y

Fig. 6 is a diagrammatic view of the apparatus for preparing and treating the mineral surfacing suspension and for supplying it to the final mineral surfacing units; and

Fig. '7 is a diagrammatic, detailed, view in end elevation of an alternative arrangement of color metering rolls.

This application is a continuation of our copending application S. N. 296,690, filed Septem ber 26, 1939, and now abandoned.

It has been well recognized for many years in the paper industry that the printing characteristics of a paper sheet may be improved by proper surface application of a finely divided mineral suspension, usually known as coating color," to the surface of the sheet. For many years so-called coated paper has been made and used, particularly in the more exacting types of printing such as multiple color reproduction and half-tone work for magazine illustrations and the like. For many years the most usual commercial pract ce, so far as known to us, was to apply a suspension of mineral and adhesive in water to the surface of a sized paper and to utilize suitable brushes to spread this suspension to provide a uniform and properly smooth film.

In such operations it was the practice to utilize a comparatively hard sized paper and a coating color of comparatively low solids content and therefore very fluid because of its large quantity of water so that when applied to the waterresistant sized surface the brushes could act to cause the material to spread to provide a uniform smooth covering film.

Some years ago applicants original assignee evolved and has made large commercial use of methods of, and apparatus for, coating paper webs, of varying weights, involving the use of metallic spreading rolls. or knife edge members arranged to provide relative movement with reference to the direction of travel of the paper and to act upon the mineral suspension on the traveling web so as to smooth and spread the mineral material adequately and produce a comparable high grade mineral surfaced sheet, and in which the coating colors were of higher solids content than formerly used and higher solids speeds could be attained.

Likewise, applicants original assignee, subsequently developed methods of and apparatuses for manufacturing and treating paper whereby mineral color suspension could be applied in and upon the surface of the traveling formed web to give a surface impregnation or a composite impregnation and light-weight coat, or a coat applied upon the surface in desired quantity, for the desired mineral finished surfacing.

Likewise use was made in the paper making industry of a printing press mechanism having usual ink rolls, operated so that the mineral pig-- mented color suspension, with greater solids consistency than ordinarily used in the coated paper industry under the other processes asdescri'bed, as in printing would be passed through such spreading ink rollers, such as used for working and spreading ink into a suitably uniform and preworked film for transfer as such to the paper, whereby to work and spread the pigmented suspension into a preworked continuous film of the proper low water content and characteristics to be delivered finally upon the printing roller which would transfer it to the surface of the paper sheet as a continuous preworked-printed According to the present invention a mineral surfaced paper product may be produced having a desired quantity of mineral material, up to comparatively large amounts, applied to and spread uniformly upon the surface of the sheet, at very high paper making speeds, to provide a product of superior appearance and printing characteristics equal to or comparable with the best products made by the other processes and yet economically produced.

In the form of apparatus shown, which diagrammatically illustrates a preferred form of apparatus used satisfactorily in operations on commercial scale, a suitable paper stock is supplied to the head box, or other form of inlet I0, for supplying the fibrous stock or furnish to the fourdrinier, or other forming wire, which is indicatedby the numeral II, and passes over the breast roll l2 and the couch roll l3, which is preferably of the suction couch type. The formed paper web is then transferred to a felt l5 for the first roll 16 of a multiple roll press, the web passing over that roll on the felt through the first nip, around the bottom of the second roll I! to'be picked up again at the second nip and passed with a felt over the third roll 18 after which it is picked off of the felt I9 and passed through the rolls of a smoothing press indicated by the numeral 20. As the practicing of the present invention makes it desirable to control in a predetermined manner the surface finish and smoothness of the paper web and also the uniformity of formation, porosity, receptivity and absorptivity thereof for the fluent constituents of the mineral suspension thereafter applied to it, and its inherent and maintained resiliency, with respect to the subsequent operations to which it is subjected, the formation of the paper itself is controlled accordingly beginning with selection of the stock or furnish from which the web is formed.

Very satisfactory operations under commercial conditions to produce a very satisfactory and high grade finished product has been secured using a raw stock furnish c0mprising Range Average Low High Material variations are permissible depending upon the subsequent pressures, constituents, consistency, freeness and fiowability of the color, paper speed, etc. The soda, sulfite, and groundwood stocks are terms well known and understood in the paper industry, such forms of pulp being generally used throughout the industry to manufacture webs of paper in which one or both surfaces are subsequently treated with mineral suspensions to produce what has been generally known and widely used for many years as surface treated or coated paper; and the term broke is likewise well understood in the paper industry to designate the commercially unusable paper which is produced in paper manufacturing as a result of breaks in the web at which time many hundreds of feet of paper may be run off by the paper machine before the operators can stop the machine and rethread it and resume the manufacture of the regular commercial paper. The broke of course contains the same amounts of the several constituent pulpsand other materials as the commercial paper, and when broke is used the paper manufacturer knowing the relative proportions of the several kinds of pulp and other constituents therein can readily determine the actual quantity of each of the several constituents which is being added. Of course, where thebroke is re-used m the manufacture of paper from a furnish of the same constituents as is contained in the broke itself, the production problem of determining the amount of broke to add is simple, and in operation skilled production men in the paper mill can and do figure the relative constituents of the furnish for any particular paper to be manufactured as part of their everyday job.

As we have found that the upper or so-called 5 felt side of the web may have pits-and irregularities which in magnitude and depth greatly exceed any irregularities and coarseness of interstices present on the wire side of the web, this undesirable condition is diminished by selecting a raw stock furnish of pulps chosen to give uniformity of formation, to have controlled freeness, and by thus and through operation of the paper machine controlling the escape of water during the web formation to produce the desired uniformity and to diminish the magnitude, frequency and depth of the pits or craters which are usually present in the top or felt side of a formed sheet. This desired uniformity and smoothness of formation may be facilitated by delaying the rate of water escape during the earlier stages of formation. Also the dandy roll 2| should be located to operate at such degree of wetness of the formed web as to add to the desired unusual smoothness or lack of craters in the felt side without advers fecting the internal formation, the porosity and absorptivity and receptivity of the sheet; and the pressure at the smoothing press should be correspondingly controlled to that same end.

From the smoothing press the paper web which is indicated by passes through a drier section, of usual construction and comprising a suitable plurality of drier rolls 21, with the drier felts 28 r and supporting rolls, drive, etc.

After the paper has been suitably dried, according to its inherent characteristics and the subsequent processing, it is subjected to a compacting and smoothing operation. This may be accomplished by the utilization of the calender 30 or the calender 3|, or both together in balanced operating relationship.

As illustrated the calender 30 is a two roll calender, and is located between two sections of drier rolls in such position in the drier section that the sheet will have been dried to a moisture content of substantially or lower, and satisfactorily down to a moisture content as low as of the order of 10%. This calender has its pressure adjusted with respect to the moisture content of the web, its formation, inherent resiliency and subsequent processing. Generally speaking the required calender pressure varies with the moisture content of the web; and for a given web the higher the moisture content the more readily the paper web responds to this treatment, 1. e. the pressures required vary inversely as the moisture content. Care must be taken to limit the amount of pressure with respect to the character of the web and to control its uniform application for a substantially uniformly formed web to avoid crushing the paper unduly and irregularly. The calender operation should be controlled to compact the paper to such extent as will leave it capable of withstanding any subsequent calendering pressures of the process without the danger of objectionable subsequent crushing of the paper and the mineral upon its surface to disrupt the continuity thereof. Also the calendering operation is conducted so as to smooth out thesurfaces, especially to sufficiently diminish the irregularities and pits of the felt side and to bring all those irregularities within the dimensions and quantitative limits of the suspension subsequently to be applied. That is, the traveling paper web is subjected to a controlled rolling operation, under pressures such. that proper smoothing of the surfaces will be accomplished and likewise the web will be compacted throughout its extent, from surface to surface, so that with the moisture content of the web and its character and formation properly coordinated with the rolling pressures, there will be such breaking down of looseness of formation throughout the body of the web as will give the desired uniformity of formation, absorbency, etc., with a predetermined retained consolidation or com-. pacting but with treatment such that the inherent resiliency of the web will not be exceeded. That is, while the rolling pressure effective upon the web will tend to smooth out any surface irregularities in the web and will also compact the body of the web, thus decreasing its thickness or caliper to some extent; nevertheless, the rolling pressure is controlled and coordinated with respect to the moisture content, and the character of formation of the web so that while its surfaces are properly smoothed and the body of the web compacted throughout prior to the application of the mineral suspension, nevertheless such compacting does not exceed the inherent resiliency of the fibrous structure of the web so as to destroy that fibrous structure and therefore the compacting is not so conducted as to completely exceed the inherent resiliency of the web and the smoothed and compacted web whl1e,thus of lesser 5 thickness or caliper and having smoother surfaces nevertheless has retained its springy or re- V --silient characteristics and when the rolling pres sure is removed it will be capable of predetermined limited amount of increase in thickness as it 10 leaves the nip of th rolls causing rolling pressure, and therefore the action is one which has been termed reversible compacting with the inherent resiliency of the web retained, rather than a compacting which is carried to such extent that 15 the inherent resiliency is exceeded and the web crushed and left so that the compacting action at the nip of the rolls giving such rolling pressure is irreversible and the web crushed and broken down because of its inherent resiliency having been exceeded.

The other calender 3| is shown located at a position where the moisture content of the paper, with the number of drier cylinders shown, would be not in excess of 10% and, with such character of raw stock furnished as described above satisfactorily, and even preferably, as low as 3% to 5% or 6%. Since the paper web at this considerably reduced moisture content range has an inherent resiliency and resistance to deformation which is considerably greater than with the moisture content range indicated for the location of the calender 30, and also greater forces are required for effecting required smoothness of surface irregularities to substantially within the 35 range of thickness and quantitative limits of the later applied color suspension, it will normally require substantially greater pressures and also a larger number of calender rolls and nips, our experience in practicing the present invention having indicated that a calender, as described herein, having usual metal rolls and using five nips and two or three weights on the lever arms, will be satisfactory with the paper web as made from the above described furnish and with moisture content of from 3% to 6% or 3% to 8%. Both calenders 30-3l need not be provided; but with both available greater flexibility in operation to meet a wider range of conditions is provided. Each calender is constructed in the usual way so that varying pressures may be exerted at the nips and so that, when desired, rolls may be opened to be non-operative on the paper. Thus either or both of the calenders may be used as desired and the paper web treated under the conditions of moisture, etc. to give most favorable results of compacting, smoothing, etc. In actual commercial operating conditions under conditions such as described above satisfactory results have beef secured when operating to produce a coated book paper when using the calender 30 with the nip pressure of the order of 135 pounds per linear inch; and when using the calender 3| with nip pressures of the order of 320-350 pounds per linear inch. The operating tolerances in the calender 30 are closer than with the calender 3|.

Having been properly compacted and smoothed to give the desired surface free from objectionably obstructing pits, ridges or crevasses, the paper web is then passed to the nip of a pair of rolls, shown diagrammatically in Figs. l-lA and Fig. 6, and more in detail in Figs. 2-5. The upper of these rolls is indicated by the numeral 35 and the lower by the numeral 36, and which are shown in greater detail in Figs. 2 and 3. 7. Each of these rolls as shown has a metal core and a rubber surface layer. The rolls are alike except for surface hardness, and the rolls in the machine illustrated and satisfactorily used in operation are approximately 30 inches in diameter-the top roll having a rubber cover Of 1 P. 31 J. hardness and the bottom roll a rubber cover of 35 P. & J. when measured with a A; inch ball. The term P. 8; J. hardness" is one which is well known in industry, such as the paper industry, which uses rubber covered rolls and is in common usage to indicate the hardness or softness of the rubber layer covering such a roll; and in the paper industry and other industries, it is common practice to order from rubber manufacturers rolls which are rubber covered by designating the character of the roll in terms of the P. 8; J. number, that number having been fixed by the rubber roll manufacturers themselves and having a well known meaning. Generally speaking, the P. 8: J. numbers involve the amount of depression made by a one-eighth inch steel ball in the surface of the rubber under a kilogram weight, measured in hundredths of a'millimeter. It is usually measured by an instrument developed by the Pusey and Jones Company which is used for the calibration of the hardness or density of rubber covering for rolls. The rolls are so constructed that the cores carrying the rubber surfaces are of extreme rigidity to prevent objectionable sagging or with suitable crowning to compensate therefor; and satisfactory results have likewise been attained using one roll, preferably the upper, having a chromium plated metal surface and the other roll a a rubber surface of the character described for the bottom roll. Also under proper conditions the rolls may be reversely positioned with the hard surfaced one below and the softer one above.

Each Of these rolls 35 and 35 turns so that its surface travels in the same direction as the paper, and they have associated with them metering rolls which function accurately to meter onto the surface of each of the rolls 35-36, be-

yond its respective metering roll, a predetermined and accurately controlled quantity of mineral suspension, so that an accurately controlled quantity of such suspension is carried on the surface of the roll into the nip between these rolls 35 and 36, where the traveling paper web enters the nip to pass between these two rolls overhead frame member 45, the opposite end of which is supported on the standard 46. There are two of these beams 45, as shown in Fig. 3, with a cross beam 41 supported between them, and generally located to be somewhat above the rolls 35 and 35 for supporting part of the adjusting and moving mechanism hereinafter referred to. Fastened to the standard 46, midway of its height is an overhanging extensionor bracket 48, which has connected to it by a suitable bearing indicated by the numeral 49, a pivoted supporting arm or member 50.

As shown in Fig. 3 there are likewise two of these pivoted arms 50, each of which has attached to it a depending bracket 5|, which includes a bearing for one end of the shaft 51, of the roll 35.

Mounted upon the floor are two standards or support members 55 each of which carries an upwardly extending bracket 58, likewise having a bearing for supporting one end of the shaft 58 of the roll 38.

The pivoted arm 50 is provided with suitable moving and pressure controlling mechanism whereby the roll 35 may be moved to or from the roll 36 so as to position them against each other with the necessary and predetermined pressure for the particular operating conditions present at the nip for the character of the paper web passing therebetween. the other conditions of the color. etc., and for the final product desired. For effecting such movement and adjustment of the member 50, and the rolls 35 and 35 with respect to each other, each member 50 has pivotally attached to it an arm or connecting rod 60, illustrated as a pair of such connecting rods for each member 50, each of the pair attached to one side of its cooperating member 50. The upper end of each pair of the members 50 is pivotally connected to a crosshead 5|. Each crosshead 8| has slidably positioned therein a shaft 62, having a collar 63 on the upper end thereof above the crosshead and another collar 54 thereon below the crosshead. A spring 65 is positioned around each of these shafts between the crosshead GI and the upper collar 63 and a spring 56 between the crosshead BI and the lower collar 54. A motor' 61 is mounted upon one of the beams 45, which drives through a suitable reduction gearing indicated generally by the numeral 58, to the cross shaft 69, which in turn is in driving connection at its opposite ends with the oppositely positioned shafts 62 so that upon actuation of the motor the shaft 69 will be rotated to cause movement of each shaft 62 against the action of the respective springs 65 and 88, to urge the roll 35 against the roll 35 with a predetermined selected pressure, or to lift the roll under spring pressure against the weight of the roll and its supporting parts to give a nip pressure between these rolls less than that which would normally be furnished by the weight of the roll and its parts. 69 indicates a hand wheel which is mounted on the shaft '59, at the end opposite from the motor, and which can be used alternatively for manual operation as described.

A spring pressed slip clutch, indicated generally by the numeral 10 is provided between the motor and the cross shaft 69 to avoid pressure shocks in operation. Also the crosshead 5| carries two pressure indicator devices each comprising a sector and an indicating finger movable wth respect thereto, the sector 15 and cooperating finger 15, which is connected by means of a flexible connection to the lower collar 64 serving to indicate the downward pressure exerted at the nip of the rolls 3536, this indicating mechanism being actually responsive to the spring compression, but calibrated to read directly the nip pressures. Inasmuch as the lower spring 66 serves, in operation, to exert a lifting force tending to rotate the member so about its pivot against the weight of the roll 35 and its connected parts, the member I5 is calibrated to read directly the nip pressure in terms of the weight of the parts which is thus unbalanced and effective to exert a nip pressure between the rolls. In the actual machine illustrated the weight of the upper roll parts gives a turning movement exerting 312 pounds per linear inch as a maximum and the and the other end being supported in any suitto the arm 58, in addition to the, turning force developed by the weight of the parts, as heretofore described. As the pressure thus exerted supplements that indicated at the member 18 is calibrated to read pressures from 260-460 pounds per linear inch up. By means of this arrangement extreme nicety of pressure control at the nip is attained.

Pivotally mounted upon each member 58 is an arm 85, the lower end of each arm carrying a bearing to support one end of the shaft of the metering roll 31. The upper end of each member 85 is pivotally connected to a crosshead 86, which is in turn connected to an adjusting shaft 81, having a collar 88 carried thereby, with a spring 88 surrounding the shaft 81 and located H between the crosshead 86 and the collar 88.

Rotatably mounted in a pair of upward extensions, one carried by each of the pivoted members 58, is a cross shaft 98, the end of which is shown by the numeral 98 in Figs. 2 and 5. This shaft, at each of its opposite ends, is operatively connected to one end of one of the shafts 81, so that it may be oscillated or swung in opposite directions and, for 'example, when moved in one direction it will act through the 5 collar 88 to compress the spring 89 against the crosshead 8'8 and thus swing the pivoted arm 85 to urge the metering roll 31 against the surface of the roll 35, with a force determined by the operating pressure thus exerted and when moved in the opposite direction will tend to lessen the pressure of the metering roll against the roll 35. In

Fig. 3 the location of this upper metering roll 31 is indicated in dotted lines. At one end the shaft 98 is connected by means of a universal joint 4 9| to an impeller shaft 82 which in turn is connected through another universal joint 9| and a slip clutch 83, which is driven by the motor 84, suitable speed reduction gearing being interposed between the motor and the friction clutch, as indicated at 95. This assembly of motor and impeller shaft, 'etc., is suitably supported by being suspended from the beam 41', which is extended in line with the cross beam 41, one end of. it being supported upon one of the members 45 able way-as by means of a bracket mounted upon the building wall, or the like.

The member 88 has attached to it a pressure indicating mechanism comprising a calibrated sector member 95, having a cooperating indicating finger 81, the finger 81 being connected by a flexible member to the relatively stationary crosshead or pivoted arms 85, this construction in effect making the finger 81 movable in direct response to flexure of the spring 89, and a spring 88 being attached to the finger 81 to urge it in the opposite direction, as a restoring spring. This sector 88 is calibrated to indicate directly the pounds pressure at the nip between the contacting rolls, in terms of nip pressures per linear inch, as is the case also with the indicating mechanisms heretofore described; and as the roll 31, as indicated, is preferably mounted so that there is substantially negligible turning mo- 10 ment due to the weight of the parts, very accurate direct pressure adjustments can be made with comparatively simple mechanism-pressures ac-' curate to the unheard of nicety in paper machine roll adjustments of not to exceed 4 pounds per linear inch.

As described, the roll 31 is independently adjustable through the pivoted arm to give the desired nip pressure with respect to the roll 85, and without disturbing in any way the setting or adjustment of the roll 35 with respect to the roll 38. Furthermore, the construction is such that the member 58 may be swung about its pivotal mounting to control the nip pressure between the rolls 35 and 36, or to swing the roll 35 entirely away from operative relation with the roll 35 for purposes of clean up, repair to the rolls or the like. This is particularly advantageous in that the rolls 35 and 36 may be thus relatively adjusted to take care of varying weights of the paper and other operating variations with out the necessity of changing the metering roll adjustment from a satisfactorily operating condition. It is in order to accomplish this that the universal joint construction of the impeller shaft 3 92 is provided, this construction permitting relative adjustment of the metering roll with respect to the roll 35 with proper driving of the cross shaft and without disturbing setting if the member 58 is moved about its pivots.

The paper web 25 passing from the calender is preferably passed over a cooled roll H8, which is freely rotatable in bearings mounted upon springs, illustrated diagrammatically at Iii in Fig. 2 and maintained under suitable tension range coordinated with the tension of the web of paper as it passes from the calender into the nip of the mineral suspension applying rolls 35-36. This roll is cooled in order to make sure that the residual temperature of the paper web as it comes from the drier cylinders is not excessive, as it goes into the color application zone. Another roll 2 is positioned just in advance of the inlet of the nip between the rolls 35 and 36 for controlling the angle of approach of the web being processed as it passes into the nip,

this roll being likewise suitably mounted for free turning with the paper, in suitable bearings.

In order to provide a proper amount of mineral suspension to be applied to and upon the surface of. the traveling web such prepared mineral suspension is fed into the nip space between the rolls 35 and 31, which space acts as a trough to receive and contain a supply or pond of mineral suspension. Inasmuch as the amount of mineral supplied to the paper web should be accurately controlled for desired operating conditions to produce a desired end product, it is preferable to maintain a substantially constant depth in the pond of mineral suspension, entirely across the length of the rolls. Furthermore, it is desirable to maintain the pond of mineral suspension or color substantially uniform in its characteristics clear across and thus to prevent irregularities and undesirable variations in operation which might otherwise result. In order to maintain the predetermined and uniform head in the pond, and also to supply the mineral suspension thereto so as to maintain uniformity of composition and characteristics clear across, means is provided for supplying the mineral suspension through a plurality of pipes or nozzles, which are oscillated back and forth across the face of the rolls, so as to continuously replenish the mineral suspension in the pond throughout its entire transverse extent. Mechanism for accomplishing this is shown more in detail in Figs. 2, 4 and 5. The prepared mineral suspension of desired composition and characteristics is pumped to a manifold II5, properly supported from the members 45. As shown, one end of this manifold is connected by the delivery pipe Hi to the discharge end of the pump whereby the mineral suspension is transferred from the machine storage tank or chest 240 (see Fig. 6 and description below), the other end being open for discharge of any excess back to the machine storage chest through the return pipe 2'63, the construction and operation being such that an excess of the color is pumped to and through this manifold M5. A plurality of pipes H6, each having a control valve ill, open out of this manifold M5, the manifold M5, and the depending pipes tit, being located substantialiy above the nip-trough between the rolls M7. By means of the individual control valves it! the amount of suspension fed through each pipe may be accurately controlled to attain the desired conditions of feed into and within the nip-trough. The lower end of each pipe IIS has a flexible tube H8 attached thereto, which in turn carries at its lower end a nozzle or pipe H9. As a means for effecting desired movement of these nozzles they are shown as passed through a plate I20 the opposite ends of which are pivotally connected to depending straps I24, the upper end of each strap being also pivotally connected to a bracket I22 attached to the stationary supporting framework heretofore described. One of the members 50 has attached to it an upstanding bracket I23, carrying a rotatable pulley I24 having a crank arm I25 which is connected by means of the rod I26 to one of the straps I2I so that upon rotation of the pulley I24 oscillating motion will be imparted to the rod I26 to oscillate the plate I20 in a direction parallel to the axis of rotation of the two rolls 35 and 31 and iongitudinally of the nip-trough. In the construction shown an oscillation of approximately 6 inches to each side is imparted to the nozzles H9 and the nozzles themselves are therefore positioned apart a distance slightly in excess of 12 inches, substantially the same as the full stroke movement of the nozzles. The pulley I2 is connected by means of a belt I21 to a driving pulley mounted upon the shaft I29, which in turn is supported in a second bracket I28, which shaft also carries a driven pulley I29, connected by means of a belt I30 to one end of the shaft of the roll 38, as ,shown in Figs. 4 and 5. By means of this construction the plate I20 is oscillated in timed relationship with respect to the rate of rotation of the roll 35, and asthe roll 31 is controlled to rotate in predetermined speed relation with the roll 35, the result is to feed the mineral suspension into the nip-trough in a relationship controlled with respect to the rate of operation of the rolls 35 and 31. This, in conjunction with the adjustment of the several valves III will give a predetermined feed of the mineral suspension, will maintain predetermined head completely across the nip-trough, and will prevent the segregation of any of the color suspension as a result of forming dead pockets so that the color in the nip-trough will be of substantially uniform composition and characteristics throughout any instant of operation, and thus by proper preparation, processing and control in handling may be maintained of predetermined, substantially constant controlled composition and characteristics for long operating periods with respect to the character, receptivity,

absorptivity, etc. of the web and the and product; or varied in controlled and selected or predetermined manner and extent as desired. The color suspension has been previously admixed into thorough uniformity and in the apparatus shown for delivering the maintained quantity to the nip-trough for working and metering need be only sufilciently fluent to be pumped to the niptrough.

The lower roll 36 is provided with a similar, and similarly operating, metering roll. The desired operating effect of this metering roll is the same as that of the metering roll 3?, as described above. And-in Fig. 75a fragmentary view, the lower color application roll, designated in this view by the numeral 36a, has associated with it a single metering roll 310:, having the same sort of operating and pressure adjusting mechanism described above with respect to the other metering roll 3!, (and therefore not shown in this view) to vary the setting thereof with respect to its color application roll 36a. However, in the operating machine which is illustrated in the drawing for example in Figs. 1 through 5,, the arrangement and location of the machine is such that greater eflectiveness of the operators in practical operation of the machine and increased safety conditions. are secured with the metering roll for the lower roll 36 placed upon the opposite side or paper web inlet side, as illustrated in Fig. 2. Therefore the adjusting mechanism for the roll 31a is not illustrated,

- and the preferred operating construction is illustrated in Fig. 2 and described in connection therewith. It is suilicient, with respect to the form of construction somewhat diagrammatically illustrated in Fig. 7, to state that the roll 31a is the same in its construction, adjustment and operation with respect to metering as the roll 31 which may be attained by obvious rearrangement of the supporting, driving and adjustment mechanism herein specifically described. As is indicated by direction indicating arrows. the surface of the roll 36a in juxtaposition to the metering roll 31a is turning downward, and consequently the surface of the metering roll 31a turns in the same direction. And this arrangement provides a nip-trough. available to receive the color suspension through the manifold IIS" and connected feed pipes. the whole mechanism being arranged to give the same control of the color suspension in the nip-through, the accurately controlled metering, etc., as described above. For purposes of simplicity of disclosure in the drawings, this means for supplying the color suspension to the nip-trough, for the lower rolls, is illustrated more or less diagrammatically, it being understood that the more desirable feature to be preserved is the supplying of the color to this nip-trough so as to cause substantially uniform head and substantial uniformity throughout the extent of the nip-trough. In this diagrammatic illustration the flexible tubes and the oscillating arms and plates for causing movement thereof are not shown; but the manifold H5 is shown diagrammatically, in practice being supported by any suitable mechanism so that it may be oscillated back and forth. This mechanism is not specifically illustrated or described in all details, since its construction and operation are the same as the correspondingly numbered parts as illustrated in detail in Figs. 3. 4 and 5 in connection with the manifold IIS and associated parts and fully described in connection therewith. For effecting this oscillation a projecting member is aseaaeo attached to the manifold, which in turn receives one end of an oscillating connecting member I (see Fig. 2) which in turn can be driven by mechanism such as that shown in Fig. 4, and described elsewhere as stated. This mechanism would impart proper oscillation to that portion of the manifold which directly serves the niptrough for the lower rolls. and suitable flexible connection would be interposed between the two portions of the manifold to permit this.

As shown in Fig. 2, however, th surface of the roll contacting with the surface of the metering roll 31 is traveling in an upward direction and consequently the surface of the metering roll travels likewise. On this account the space above and between the two rolls is the discharge space of the metering nip instead of the inlet space in contrast with the other two conditions described.

In order to provide for maintaining the same uniform and accurately controlled composition and characteristics of the color suspension to be metered onto the surface of the roll 36, a second roll I is provided and so mounted that it may be pressed against the roll 31' as desired.

Supported upon the standard or supporting member 55, at each side of the machine, by a suitable pivot bearing I, is a, roll supp rting member I42. Each of these members has attached to'it an upstanding extension I43 which carries a bearing for the corresponding end of the shaft of the metering roll 31. Each member I42 likewise carries an extension I44 which is pivotally connected to the member I42 by means of a pivot bearing I45, each such upwardly extending pivoted member I44 carrying a bearing for one end of the shaft of the roll I40. The

pivoted member I42 also carries a-lower cxtension which is connected by means of a pivot I46, to an adjusting shaft, which is surrounded by a spring located between two collars, these parts being enclosed within a housing I This mechanism is likewise operated by a suitable motor and gear reduction indicated generally by thenumeral I48, driving cross shaft I48 (see Fig. 3); and has pressure indicating mechanism indicatedgenerally by the numeral I49 and calibrated to indicate directly the pressure conditions at the nip of the rolls 36 and 31, the construction and operation of such part being as described above in connection with rolls 31 and 35.

Pivotally attached to the upper end of the extension I43 is a, shaft or rod I50, the opposite end of which carries a hand wheel I5I, which, upon rotation, actuatss the spring containing cylinder I52 to move it axially of the ,rod I50. The

cylinder I52 is a cup shaped member with one end of the spring resting against a bottom or suitable internal flange therein, the other end of the spring resting against a, collar I53 carried by the rodI50. The cup shaped member floats on the rod I50 and has a knife-edged type of pivot member indicated at I54 to be located within a corresponding notch in the cooperating face of the upward extension I44 which supports the roll I40. By turning the hand wheel I5I pressureis exerted upon the spring and transmitted to the cup member and its pivots I54 to press against the extension I44 and swing that extension about its pivot I to urge the roll I 40 toward to roll 31' under the desired tension pressure of the spring. Means for feeding the color suspension to the nip-trough between the rolls I40 and 31', and maintaining a desired predetermined head and uniformity of composition and characteristics of distribution of the color within the nip-trough is provided which means is substantially a duplicate of the means described above, the color supplying manifold being indicated by the numeral 5', the flexible pipes 8' for permitting oscillation of the nozzles H9, and the other parts corresponding.

As is the case with the mechanism described in connection with the upper roll the pivoted member 142 carries both rolls 31' and I40 so that the parts may be moved as a unit about the pivot I4I to vary the position of the metering roll with respect to the color application roll 36 without disturbing the relative setting of the rolls 31' and I40; and likewise the roll I40 may be given independent adjustment without effecting the setting at the metering nip.

The color supply maintained in the nip-trough is carefully controlled with respect to its solids content, its adhesion-tension for the surfaces of the rolls 3535 and also for the paper web, its freeness, the receptivity of the sheet for the mineral suspension and the various constituents thereof, its consistency, its thixotropic characteristics, etc., so that in operation an amount of color is metered between the two rolls 35 and 31 which is such that there will be maintained upon the surface of the roll 35, as it approaches the nip and the paper therein, an amount of color suspension slightly in excess of the amount to be applied to remain on the surface of the web 25 as it passes from between the rolls 3536. Like controlled conditions are efi'ectuated with respect to the color applied to the surface of the roll 33 to be carried up into the nip and to the paper web.

- The color as introduced to the nip-trough is of very high solids content, ordinarily ranging in commercial operations from approximately 40% up to 56%, generally of the order of or somewhat more, and even somewhat higher than 56% when desired. A color suspension which has been found to function very satisfactorily in the practicing of this invention, utilizing the equipment above described, is of the following composition:

Per cent Stayco 14 Domestic clay 41 English clay 41 Ammonium oleate 2 Calgon 1 Such color gives satisfactory results in the practicing of this invention when admixed with water to having a solids content of approximately 52% to 56%.

A suitable casein containing color, which has likewise been used satisfactorily. is as follows:

Per cent Casein 3 Stayco 18 H. T. clay 39 Satin H. T. clay 38 Ammonium oleate 1 has been processed and treated also to remove large particles and extraneous matter and to give a different grade of clay for use in the paper coating industry, and is prepared generally according to the process disclosed in U. S. Patent to Maloney No. 2,158,987. The term domestic clay is used to differentiate clays comin from American clay deposits suitably processed for use in the paperindustry, such as the H. T. clay and Satin H; T. clay above referred to, and clays of somewhat different characteristics which have also been long used in the paper industry, including that part of the industry relating to the coating of paper, and which are derived from clay deposits in England.

Stayco" is a trade-name for a thin boiling oxidized starch made by the Staley Manufacturing Company, a satisfactory oxidized starch as referred to hereinafter.

Calgon is a commonly accepted trade name for a sodium phosphate (such as hereinafter referred to) developed for water conditioning, its properties beingspecific gravity 2.5; refractive index 1.485. It is insoluble in organic solvents, mutually soluble with water in all proportions. In water solution it binds various metallic ions tightly in soluble complexes, particularly calcium. It coagulates albumens. It disperses finely divided metal oxides and salts. It inhibits crystallization of slightly soluble compounds such as calcium carbonate, and calcium sulphate. And though essentially neutral in solution it reverts to acid orthophosphate very slowly at ordinary temperature and very rapidly about 100 C.

Ammonium oleate" is a chemical compound, and data with respect to it may be found in any comprehensive chemical text book or dietionary.

Th term "consistency" herein is used to indicate that property which may be caused to be present in a liquid suspension or gel by proper selection of its constituents whereby a shearing stress acting thereon produces within the liquid or suspension a change in its state of fluidity or flowability the amount of change having relation to the rate of shear. Viscosity, as the term is ordinarily used to indicate the degree of flowability of a liquid or liquid suspension, should not be confused, herein, with the term consistency; for while the consistency and viscosity of a given liquid under given conditions may be the same, viscosity" as used herein is a straight line function, expressed in poises, which does not vary with the rate of shear. Whereas consistency is a variable one, also expressed in poises, in which the variation in poises expresses the ratio of the shearing stress acting on the liquid or suspension to the rate of shear. Or, consistency isthat property of a liquid or liquid suspension by which it resists permanent change of shape; and, therefore, if

till

a shearing stress is imposed whereby this retropic materials the flowability is a variable curve function with the increase in flowability being determined as the ratio of the shearing stress to the rate of shear which it produces, and the magnitude of the ratio (and the increase in flowability which is the result) is measured by the rate of shear which is produced in the liquid. We have found that in certain liquidmineral suspensions, a very thick suspension which ordinarily would be termed very viscous or non-flowing mineral colors, in the paper making industry, may be changed by such shear working, as by a rotating roll and the shearing stress it produces, to a fluent readily flowing one.

The consistency of the color at this point in the invention should be such that despite its high solids content it may be pumped through the nozzles II9H9 and to spread out to give uniform distribution and head throughout the pool in the nip-trough. Furthermore, its trixotropic characteristics are controlled by the uniformly admixed constituent materials so that the working in shear from the contacting rolls will change its state of flowability as metered to one having a viscosity reading of as low 'as 50 poises or lessthe first example given above having its viscosity reduced at the metering nip to approximately 32-33 poises in actual commercial operations despite its high solids content and normally high viscosity. This action is immediately to reduce the viscosity of the metered color and to complete the coating action so that the color metered onto the application rolls will be applied to the paper web, and will flow or spread readily and uniformly on the paper web under the action of the application rolls and will even flow to some extent on leaving the nip and separating from the roll to give uniform and smooth film surface, despite its high solids content and comparatively low water content before it reverts to its normally high viscosity. This is accomplished by preparing the color suspension of materials so selected and processed that the unusually high flowability with respect to high solids content is attained by predetermined working in shear and is coordinated with the characteristics of the web, its speed of travel, the character of the rolls and the relativeadhesion tension.

In each of the color suspension formulas set out above a material, such as the sodium metaphosphate specified, is used which has a defiocculating eifecti. e. a comparatively small amount thereof very substantially increases the flowability or fluent characteristics and the wetability, so to speak, which means the capacity of the fluid to wet the paper web despite the restraining forces which would otherwise be effective in a suspension of such high solids content.

In addition the color compositicn is chosen to be of high thixotropic character so that the material may be quickly brought from its normal condition of high viscosity and impracticably low flowability to a condition of tremendously increased fluidity and flowability predetermined as satisfactory for the various controlling operating conditions. Thixotrcpy is determined astoits degreebymeans ofascientific instrument known as the McMichael viseosimeter, a known scientific instrument. Through the use of this, consistencies are determined at two difi'erent speeds of the instnnnent and may then be calculated to give the degree of thixotropy. In the present invention thixotropy is expressed asthe ratio of consistencies (i. e. relative viscodties) at 4.5 R. P. M. to 40 R. P. M.; and in the illustrations of color consistencies given above the first formula gives a consistency at 4.5 R. P. M. of 80-135 noises and at 40 R. P. M. of 20-50 poises. This gives a thixotropy, expressed as the ratio of consistencies of 4-2.7. The second formula gives a consistency at 4.5 R. P. M. of 75-120 poises and at 40 R. P. M. of 16.5-26 poises for a thixotropy of 4.55-4.53 which is to say that the constituents of the color suspension have been so chosen and compounded that when subjected to the successive processing steps and maintained in uniformity of condition at the nip-trough the final working in shear at the metering nip will deliver the metered quantity of color to the paper at the nip of the application rolls in said state of relatively high fluidity and flowability, despite its very high solids content, and will permit of securing the required uniformity of distribution upon and incorporation with the surface zone of the paper web. The above reference to the use of the well known McMichael viseosimeter acting at two arbitrarily selected speeds of 4.5

R. P. M. and R. 'P. M., upon the two color formulations set forth above, and more specifically described later in the specification in connection with the description of the manufacture of the coating color starting with theconstituent materials, is merely for illustrative purposes; and the different viscosity readings for each coating color at the two abritrarily chosen speeds of 4.5 R. P. M. and 40 R. P. M. represent the viscosity readings of a McMichael viseosimeter at the two operating speeds indicated acting upon each particular color formulation. And from those two readings the ratio of consistencies can be determined as stated, and these ratios will indicate decreases or increases in viscosity readings which would be shown for either higher or lower R. P. M. of the McMichael instrument. It is, of course, well understood by skilled physicists and physical chemists and others scientifically and technically skilled in the practical manufacturing fields of industry that the viscosity reading indicated by the McMichael viscosimeter for liquids or suspensions which have varying viscosities at diii'erent rates of shear is according to a scale, and if the R. P. M. of the McMichael were reduced below 4.5 then the viscosity reading for the two color formulations would inso crease according to the thixotropic characteristics of those color suspensions and, likewise, if the R. P. M. were increased above 40 the viscosity reading for each of the color formulations referred to would decrease below the illustrative figures given'for 40 R. P. M. It is evident, however, from the explanation of consistency as used in connection with variable or temporary viscosities in a thixotropic suspension, due to working in shear, that the rate of 70 the color applying nip,

ities are attained, with such-high solids con-' the first formulation referred to will vary over a wider range than is the case with the second formulation which uses casein as an adhesive. This discussion shows clearly to' one skilled in the held of coating paper webs. that a color suspension of substantially the same solids content but having a phosphate such as Calgon which falls within the group of alkali phosphates, as referred to in column 16-, and which materials are recognized herein as dispersing agents for controlled affect upon the thixotroplc characteristics of the coating color suspension, has such effect upon the suspension of-minerals and starch adhesive that varying the rate of working in shear will cause greater variations in the viscosities corresponding to varying rates of workingJn shear than is truewith a coating color suspension using casein as an adhesive, although the casein itself is recognized as having such substantial dispersing powers so that the phosphates need not necessarily be used.

And by adequate working in shear under high pressure for even the short time interval during which the coating color is subjected to working in shear at the metering nip and also .at actual temporary viscose tent compositions, that the temporary viscosity will be brought down to a reading as-low as 1.1 to 1.7, as fully disclosed,. mathematically and by discussion of principle of operation, in the copending application of Rudolph N. Griesheimer, Serial No. 436,371, filed March 26, 1942, now Patent No. 2,392,662 issued January 8, 1946. The viscosity readings given for illustrative purposes in explaining the ratio .of consistencies, above, are not intended to be limiting in any way except as indicating a range of viscosity. read: ings well within the capacity of the long available McMichael viseosimeter, to permit the manufacturer of coated paper webs to determine that suflicient drop in temporary viscosity could be secured through working in shear using the principles of the present invention and the preferred embodiment of mechanism disclosed, despite such high solids content as would have been considered entirely impossible and impractical to be used with any form of coating mechanism, or any process of coating, prior to applicants invention.

In connection with each of thenip-troughs a dam or weir I" is provided at each end of the nip-trough so that the level of the mineral suspension, and therefore the head at the metering nip, can be maintained as desired. -In actual practice satisfactory results have been attained with a head of about 22% inches in the niptrough. Any excess is led away, and if desired can be returned to the machine storage chest.

However, with the upper roll 35 the rate of,

feed to the nip-trough can be so regulated as to substantially correspond to the rate at which the mineral suspension is applied to the paper, but an overflow pipe can be provided if desired or a save-all pan as illustrated in connection with the lower roll 36. In controlling the amount change in viscosity as the speed of the measuring instrument is increased or decreased will vary according to the constituents. Thus it is evident that the ratio of consistencies stated as determined in the coating color suspension of of mineral suspension, in the particular arrangement of rolls shown in Fig. 2, the roll I 40 is positioned with respect to the metering roll 31' so as to permit an amount of mineral suspension to go through which is in excess of that which is to be metered onto the surface of the roll ll. As a result the adhesion tension carries this excess upwardly into the lower nip between the rolls 3' and 31', to maintain a substantial excess 19 or pool therein. It is unnecessary that the amount of suspension being fed into this pool be measured with any extreme accuracy as any surplus merely drips downward and is caught in the save-all pan IGI, that pan being supported from the standard 55, and any color dripping into it being returned to the machine storage chest. Under the conditions described and for a paper speed of 450 feet per minute, with a web, or raw stock, of 40 pounds per ream of 500 sheets 25 x 38 inches, having its absorptivity so adjusted with respect to the freeness of the color that at such speed there will be suitable penetration and setting of the color before contact with succeeding rolls, when color solids content and consist ency are adjusted with respect to the roll settings, etc., to produce a coat weight of 15 pounds per ream divided equally on the two sides, the

headers ll5ll5' are each satisfactorily of 3 diameter and the pipes 6-! l8 and nozzles H9 of %-'l", and the suspension pumped to the headers to be under a pressure of 2-3 pounds per square inch. By the term "freeness as used herein with respect to the color suspension is defined the ease with which the color parts with its fluid when in contact with the paper and it is measured or expressed as the time in seconds required for the water to penetrate through a piece of standard blotter paper or raw stock when placed on the surface of the color suspension. A free color gives a very low reading while a slow color requires a comparatively considerable time for penetration. Generally speaking it may be said that all the constituents of the color may have effect upon the freeness and by suitable selection and preparation the freeness may be varied within desired practical limits. Ordinarily the minerals and adhesives used have the most pronounced and easily controllable effects upon freeness. The actual effect in many instances must be determined by actual trial. For example freeness attendant upon any clay may depend entirely on the source and method of manufacture of the clay. Bentonite, which is a very hydrous clay of itself has high waterbinding power and therefore tends to give low degree of freeness, whereas a calcined secondary kaolin such as that known commercially as Satintone has very little, or practically no, water binding power and so tends to high freeness. Other clays generally fall between 'these extremes. Also the method of dispersing the clay can change its freeness and the transfer of adsorbed wa er from clay to starch, and vice versa, may completely reverse the water-binding power, or freeness, of the system. Thus a clay which is very free when dispersed in water may result in a very slow coating color upon addition of starch, and, conversely, a slow clay may result in a free color upon addition of starch. The freeness of the finished color can not be predicted from the freeness of the various components but is the result of the combined actions of the various constituents in the presence of and upon each other. Generally speaking, crystalline minerals, such as calcium carbonate, gypsum, blanc fixe, etc., which are sometimes used in coating suspensions increase the freeness of the color, and are all comparatively very low in water-binding power.

Likewise, the water-binding power of adhesives depends upon several factors. Starches are hydrophylic (have high water-binding power) in character and bind water quite readily. But the extent of the water-binding is dependent on the kind and amount of conversion given the starch in preparing it for use. In general. the greater the extent of conversion, the higher the freeness. Addition of other materials such as clays or certain chemicals (such as borax or formaldehyde) will change the freeness of starch appreciably. Casein is another hydrophyllc colloid used as an adhesive in coating colors. The freeness of casein is dependent on the method of solution. (This is also true of other properties of casein, such as viscosity, oil adsorption, adhesive strength, etc.) The addition of other materials to casein solution, as with starch, results in various changes in freeness.

In practice, the freeness of coating colors may be adjusted between fairly wide limits by proper choice of materials. If a slower color is desired, bentonite or under-converted starch may be added to bring about this result. To produce a free color, such things as carbonate or other crystalline minerals may be used, or a clay with an inherently lower water-binding power may be selected.

In any event, the best operation is obtained in the practicing of this invention when the freeness of the coating color is adjusted to the adsorptivity and receptivity of the paper stock being used as described herein. If other conditions are the same and the same end product is desired a very receptive paper web requires a slow color, a. resistant sheet requires a free one. The range of freeness used satisfactorily in actual operations has been from 20 to 80 seconds, and very satisfactory operations being secured in commercial operations with a freeness of 35-40 seconds at the first mineral application device and 30-35 seconds at the second, measured as above described.

The upper roll 35 is driven with a motor I which has control means which causes it to drive the roll to give a surface speed which approximately corresponds with the surface speed of the paper passing through the nip. This motor drives this roll through an impeller shaft I56 having universal joints therein and a reduction gear. to permit of adjusting movement of the upper color application roll with respect to the lower while permitting adequately controlled driving thereof. Thelower roll 36 is also driven at substantially this same speed by means of the motor I58 and connecting drive shaft l5! and reduction gear; but where rolls of such substantially varying hardness in their surface layers are used,

as described above, and under the pressures referred to herein, the deformation of the softer surface layer may result in such variation of roll diameter that appreciable variations in rotational speed may be required to give surface speeds sufliciently alike to get the desired operating conditions although material variations in surface speed in the nip may occur without any objectionable operating results provided the speed variation of a roll surface and the paper surface cooperating with it do not differ by too wide a margin. In the actual commercial operations hereindescribed the rolls 35 and 36, under pressures giving a nip width of approximately 1 inches, as described, are driven at such speed that the upper roll has a normal surface speed of approximately 5 feet in excess of the surface speed of the lower roll.

The lower roll 36, in the particular machine described and operated, is driven by the individual motor I58 which is interconnected by suitable synchronizing control, with the synchronizing mechanism for the remainder of the paper machine, so that this particular roll will have a surface speed properly coordinated with the speed of travel of the paper web 25, as it travels through the machine. Any usual'form of accurate synchronizing mechanism may be used for this purpose and therefore it is shown only diagrammatically and designated by the numeral Ill.

When it is the lower roll 38 which is connected with the synchronizing mechanism in this manner, the upper roll 35 will then be driven by the individual motor illustrated diagrammatically and marked I55, any suitable form of motor control adequate for giving the desired rotational speed to the upper roll with respect to the paper speed and the speed of the lower roll being usable; and on the roll 35, as with each of the other rolls which is .movable in operation or adjustment, somesuitable form of universal connection in the drive, such as that described above, should be utilized. The motor drive for this upper roll is preferably so controlled thatthe surface speed of each of the color application mils 3H! is substantially the same as the paper speed. The rolls 31, 31' and Ill! each is likewise driven by an individual motor designated respectively by the numerals I82, I63, I64, having suitable speed and torque control so that definite surface speed relations may be maintained as desired between any two cooperating rolls, to maintain such speed and energy transfer relationships at the nip as to provide predetermined working in shear to the color and prevent objectionable variation in v the consistency of the color suspension as a result of such additional shear working at the nip.

It is, generally, desirable that the paper enter the nip of the color application rolls by going straight in with substantially the same surface contact on each side as it enters. However, this condition is extremely difflcult of attainment, and for practical operations very satisfactory results have been attained with the arrangement shown in Fig. 2 wherein the roll 2 is positioned only a short distance in advance of the hip and the paper web passed thereover so that it is brought into the nip at a slight angle and preferably contacting the harder oi the two rolls. Furthermore, because of irregularities in the sheet due to irregular stretching or expansion as the formed paper web is being dried while passing through the machine which ordinarily causes the central part of the paper web to lengthen with respect to the edges, it is desirable to have the roll H2 provided with a substantial crown which facilitates feeding the paper smoothly and without any wrinkles into the nip.

In addition it is desirable that the paper so directly out from the nip on the exit side as wrapping of either roll tends to introduce irre ular and unpredictable conditions of worming, pitting, lining and the like, each of which conditions is indicative of lack of desired smooth finish in the mineral surface. As shown each member its freeness, etc, before the mineral treated surfacepassesintocontactwiththefirstdrier roll 21.

Whereas in feeding the paper into the nip it is preferable to feed the paper as shown in Fig. 2 to slightly wrap the upper, hard roll in order to avoid fluttering or dancing of the paper which is apt to occur if the web is merely led directly into the nip, in leaving the nip it is found that the paper has a definite tendency to wrap one roll in preference to the other, usually the hard or wetter roll, and furthermore that wrapp ng of a roll gives increased tendency toward the irregularities mentioned. This tendency, as a result of the adhesion tension is sufficient to cause the paper to wrap me of the rolls, at least at times, despite the utilization of the roll I! I, which is positioned sufficiently far from the nip of the rolls to avoid defacing the ,mineralized surface after it is properly applied. To overcome this tendency, perforated or slotted air pipes it! are located closely adjacent the exit of the nip to blow air against the opposite sides of the web and thus cause .it to lead out of the nip without dancing or wrapping. The pipes are spaced slightly apart to permit free passage of the paper web between them without contacting either. Each of these air pipes I is connected to a suitable source of supply of pressure air so that a flow of air is introduced into the nip on each side of the paper web and between the web and each roll to provide sufficient air buoyancy to float the web directly out from the nip and pre- It has a depending support I10, carrying suitable bearings for rotatably supporting a roll I'll, this roll being positioned a suitable distance from the nip of the color application rolls, and located so as to lead the paper directly away. Also this roll is preferably water cooled. As thus located the water cooled roll tends to cool the air and collect a film of condensed moisture on its surface which acts to prevent the mineral material upon the surface of the paper from adhering to it and gives that mineral surface an adequate time properly to set, due to the absorptive action of the paper, the thixotropic character of the color,

vent any objectionable tendency to follow either roll. While this arrangement is not necessary, the conditions at the exit of the nip should be so. controlled that objectionable wrapping of either roll, with undue worming and the like, beyond the inherent capacity of the color to flow to subsequent smoothness, should be avoided. As shown each member I8! is a pipe extending across the machine with either a slit therein or holes so that a sheet, or a plurality of streams, of air may be introduced. Furthermore, when desirable and especially for higher speeds, means are provided, one on each side, so as to blow drying hot air upon the mineral treated sheet to cause more rapid drying and setting of the web before it passes to the first drier roll. The surface of the sheet as it leaves the nip of the color suspension application unit is wet and tacky and suiiicient time or treatment must be Provided in. order that this condition may be so modified that there will not be objectionable depositing of the color on the drier rolls. The air drying and setting of the color to secure this desired operatin condition is due in part, of course, to mere evaporation of the liquid as the paper passes through the atmosphere; but at the high Pap r speeds used this is greatly expedited by the air flowed against the surface and the character of the color as to its evaporation. Also the receptivity of the sheet and the freeness of the color must be so adjusted relatively that there will be sumcient, prompt, penetration of the water and adhesive into the paper web to produce a good bond between coating material and rawstock. the absence of which results in scaling and flaking of the mineral surface. By properly controlling the freeness and-paper web characteristicsthe color and the air drying satisfactory drying and setting may be secured to avoid any objectionable effect of the drying rolls on the mineral surface.

The mineral suspension or color hereinabove aseaaco referred to, which is delivered into the nip-trough between the rolls 35 and 31 and between the two rolls 3'! and I40 is carefully prepared to have the composition and characteristics as to consistency, flowability, freeness, etc. as above described in coordinated relationship with respect to the web of paper which is being treated. Apparatus for preparing this suspension is illustrated diagrammatically in Fig. 6. As stated above the suspension has its various constituents selected, each with respect to the other, to give the conditions in operation whi h are desired to produce the proper end p oduc A suitable paper aking clay, of proper selected grade, is preferably used, especially where a mineral suspension is desired which has less freeness than would be true with a suspension utilizing finely divided calcium carbonate to control its freeness, such as a. carbonate precipitated under controlled conditions to give the finely divided material which is to some extent used in the paper industry. Also English clays, generally speaking, are preferable to domestic clays where the formation, compacting and smoothing, of the paper sheet are less satisfactorily performed with respect to smoothness of surface inasmuch as these clays seem to be somewhat more readily deformable in their response to calendering and therefore these clays seem more readily to spread under calendaring action to tend to fill up some of the uncorrected irregularities resulting from undue irregularity in the surface of the sheet, even after the mineral suspension has been dried to specified commercial moisture percentage of 3 to 5%. However, it is especially desirable that the paper web be so formed that its irregularities, as to depth and also as to lateral extent and quantitative capacity of any depressions, shall be maintained within dimensions or limitations which are within the quantitative dimensions as to thickness of applied layer of mineral suspension and the volume thereof available for lateral spread. It is not at all essential that the mineral suspension metered on to the color application rolls 35 and 35 be spread as a uniform film thereacross, but on the contrary the suspension may be in quite apparent ridges, of irregular spacing, provided the mineral suspension is of such character and the surface irregularities of the paper web of such limited depth and lateral extent that the quantity of mineral thus metered upon the surface of the applying roll may be suitably and uniformly spread as the paper passes through the nip to give the desired uniform film.

For purposes of illustration the preparation of the mineral suspension will be described with relation to the utilization of a domestic classified clay such as that known commercially as Satin H. T. and a No. 1 grade English coating clayas mentioned in the illustrative formula above both being selected for their flow properties in the suspension. Referring to Fig. 6 a suitable clay mixer 20!! is provided, which has kneading devices therein for thoroughly mixing and kneading the ingredients introduced into this mixer. with reference to actual operations successfully used commercially under this invention and which give color formulas approximately those illustrative ones set out in column14, the clay is fed in desired amount into the kneading machine 200. For a 2000 pound batch of suspension of the formula referredto above approximately 1700 pounds of clay dry weight is introduced into the mixer 200 along with approximately gallons of water. At the 24 agent, such as the compound of the chemical group known as alkali phosphates, such as sodium meta phosphate or sodium pyrophosphate, a satisfactory commercial dispersing agent of this group being that known commercially as Calgon, is mixed up in the agitating vessel 2M, at a concentration of approximately 2 pounds of Calgon per gallon, which makes sufficient dispersing solution for several batches of mineral suspension having the clay content mentioned. 10 gallons of such Calgon mixture (the equivalent of 20 pounds dry weight) is added to the clays and water in the mixer 200, where the several constituents are mixed for approximately a half hour.

Meanwhile a solution of starch, which may be one of the relatively thin boiling starch such as that known commercially as Stayco, which is an oxidized starch, has been prepared by introducing 3000 pounds of starch into the starch wetting tank 2 l0, where the 3000 pounds of starch is agitated in 510 gallons of cold water for 30 to 60 minutes. The starch is then pumped, by means of a pump such as the centrifugal pump 2 into the starch cooking tank 2l2 where live steam is added through the pipe 2" and the mixture of starch and water is cooked up to a temperature of 0., this maximum temperature being maintained for approximately 15 minutes. The starch isagitated and thoroughly mixed while cooking, and is preferably passed through a suitable screen such as a rotary screen, before it is fed into the cooking tank. The quantities just mentioned makes sufficient starch for about nine batches of mineral suspension for the paper speeds, coat weight, etc. described above. Having been thus cooked, 108 gallons of this cooked starch (300 pounds dry weight) are dropped by gravity into the starch cooling and measuring tank 2 I 5, which is provided with an agitator, 2i5', capable of keeping the starch thoroughly agitated. From this tank 215 a part is fed to the mixing tank 200 by means of a suitable pump 2l6 through the pipe 2 l1. Satisfactory results are secured by adding 35% of the batch of starch at this stage which equals approximately 37 /2 gallons or approximately pounds dry weight. The starch when thus introduced facilitates emptying the clay which has been thoroughly kneaded in the comparatively small percentage of water, the mixture being dumped from the tank 200 into the clay make-down tank 220 which also has agitating or mixing mechanism 220.

Meanwhile a suitable mixture having lubricating properties has been prepared in the tank 22I, oleic acid being a suitable such lubricant. Ammonium oleate is likewise suitable. In preparing this lubricating agent, ammonium oleate for example, it is mixed in the proportion of 2 pounds per gallon, with suitable agitation by the agitating mechanism 222 of suitable high speed agitating type, a similar form of agitating mechanism 20! being used in the tank 20!. Of this mixture 25 gallons is now added to the clay mixture in the tank 220 and resulting mixture agitated for approximately 15 minutes. This material effects desired controlled modification of the adhesion- 'tension of the suspension for the roll surfaces, and causes proper decrease in the tendency toward wrapping the roll and likewise greatly decreases the tendency toward worming which has been found to accompany too great adhesiontension. mix is then dropped into the blend tank 225, through a suitable wire basket screen, and in thisblend tank the balance of the starch same time a mixture of a suitable dispersing 75 withdrawn as a batch into the tank 215 is added 2s and the mixing continued, withtborough agitationbytheagitatorflflandinthistankfora periodofzhours. Thisagitatiomwiththemate rialsusedgivesaworkinginshearwhichgreatly dec. the consistency and so the ilowability of the mineral suspension, as a concomitant of its 1 thixotropic charactenand'afterthhmixinginthetankflithe material is pumped by means of a positive displacement pump of the type known commerciallyas Moyno" and as indicated tically by the numeral 22. the material being pumped through the pipe I" to a roll mill 228.

This mill 228 may be of suitable character. such as those used in various industries for working pigments in suspension, such as the well known so-called ink mill." The blended color from the pipe 22! flows into a hopper 22! and by gravity through an intermediate tank 235.

having a sloping bottom, no agitator being necessary to use in this tank. This sloped bottom feeds the material by gravity toward the discharge outlet to which is connected the inlet of the pump 236, also suitably the so-called Moyno type, which pumps the material to the machine storage tank 2 which is substantially a duplicate-of the blend tank 225 and has a suitable agitating mechanism Ill as indicated in dotted lines, for maintaining the suspension in thoroughly agitated condition. From the tank R the material is pumped by another Moyno pump 245, through the pipe iii which in turn is connected to the inlet end of the manifold iii and thence flows through the associated mechanisms at the desired rate controlled by the setting of the valves ill into the nip-trough. A coating color as so prepared has a solids content within the range of 52-56%, and approximately 53%. Preferably suitable strainers are located in the pipe 25L two of these strainers being shown, the strainer Iil being of the so-called Saree type, which is a commercially well-known apparatus, this strainer being driven by the motor 2. This Sarco strainer has two outlets one connected to the pipe and from that to the manifold i ii this outlet serving to pass the desirably selected material, the other being connected to a pipe 82 through which any rejects maybe passed into the save-all pan I. Likewise a by-pass pipe 2st is provided having ahand operated Sarco strainer 26! which has two branches connected respectively to the manifold H5 and to the reject pipe 262, so that the hand strainer may be used alternately or at the same time with the motor driven one. Preferably the motor driven strainer III is used, but after a reasonable period of use, usually about eight hours where the other operations in the preparing of the suspension are adequately carried out,

thestraineriscleanedandatsuchtimethehand operated strainer in the by-pass pipe may be utilized while the motor driven strainer is being thus cleaned.

Ifitisdesiredtousecaseimasinoneofthe illustrative formulas set out above. the procedure gg-nretered to the color application rolls 35-46 isconditions the casein is prepared in the casein kettle fll. Cold water is first added to the casein kettle throughthe pipe 21] in the proper amount for cutting the casein according to the color formula chosen and the casein is then introduced. The water casein mixture is mixed for 30 minutes, after which the alkali is added and steam turned on through pipe 212. Cooke ing is continued until the temperature reaches 40-45 C. The casein is then cooled gradually and can be dropped from the casein kettle into the blending tank 225, in the desired proportion.

Preferably measuring tanks 280, of proper volume, are used to facilitate feeding the liquid ingredients.

The excess color from the nip-trough, and from the save-all .iil, is returned to the machine storage chest I, as indicated at 215. Bymeans of the mechanisms thus described the composition and characteristics of the mineral suspension is maintained uniform, and under uniform head. entirely across the nip-trough and the excess color is returned to the machine chest. where the agitation thoroughly mixes it'with the other mineral within this chest so that the suspension maintained in the nip-troughs and always of the predetermined character adapted to the characteristics 01 the paper web, its formation. its receptivity and absorptivity, and the nip pressure. The pressure between each metering roll} and 31' and its corresponding color application roll 35-", should be'accurately adjusted to give the operating conditions desired the mechanisms described above giving extraordinary nicety of adjustment of the order of 4 pounds per linear inch. The quantity of solids applied to and upon the paper web as it passes through the nip is'best controlled by properly controlling the solids content of the suspension. However, the pressures at the nip of the rolls 3536 must be maintained within suitable operating range for most desirable results, the best results for wide variety of conditions being of the order of 90-175 pounds per linear inch. The pressures at the nip are critical in that there is a certain minimum pressure for a sheet of given characteristics below 7 which satisfactory operations will not be secured.

but a rough surface will ensue with insuflicient spreading and equalizing of the coating as applied to the paper. This minimum has been found to be about 40-45' pounds per linear inch for papers made from a furnish such as described above. and with rolls having the surface layers of the character described but for satisfactory commercial operations pressures substantially in excess of this minimum, and generally within the range of -175 pounds specified, are preferably used. Also there is a critical upper limit of pres sure above which increases produce a pattern of 1 the raw stock irregularities and also may effect the inherent chara'cteristicsof the sheet under the pressures and with the conditions of the or sheet under its absorption of fluids and the like, so that undesirable blackening may show up in is similar to that described above. Under such subsequent calendering. Such poorer results 27 have been obtained in operations using pressures above 275 pounds per linear inch.

A color suspension of the first formula specified above will have a solids content of approximately 56%, and with this suspension the paper may readily be coated to provide a coat weight of 15 pounds per ream of 500 sheets 25x38 inches divided equally upon the two sides of the paper. By increasing this percentage of solids even heavier coats may be applied satisfactorily.

If it is desired to apply a second coat, which may be particularly desirable where very heavy weight coats of the order of 20 pounds or more divided equally between the two sides are to be produced, an additional color applying mechanism may be utilized as illustrated in Fig. 1A, where the color application rolls are indicated by the numerals 35" and 36", the other parts of the mechanism being the same in construc tion as those heretofore described. Where this second coating operation is to be used the formula of the mineral suspension is somewhat different from that used on the first inasmuch as satisfactory results may ordinarily be more readily obtained if this second coating is of somewhat lighter weight than the first and also if the color has somewhat less mineral and more adhesive or sizing material. For a single coat, as described above, the solids contents will ordinarily be satisfactory if ranging from 52-56% of solids with starch as the adhesive. The formula for the second coat contains also casein and on this account, and for the reasons described above, the second formula contains a smaller quantity of solids, of the order of 43-45%,

and the somewhat increased percentage of adhesive. Also quite satisfactory results and end products may be attained if the mineral suspension first applied is of a formula comprising nearly all of the mineral solids applied and a greatly reduced amount of adhesive, and the suspension applied as the second step comprises only a small amount of mineral and nearly all of the adhesive or sizing constituent. For example, the formula for the first treatment may satisfactorily comprise 52-56% of solids; with the second treatment formula containing 43-45% of solids. We have found that such high minerallow adhesive constituent will give a mineral surface which is quite smooth and has great reduced tendency to worming, etc. Where a second coating treatment is applied the paper is then passed through the additional drying unit illustrated and containing the same sort of drier rolls 2'! and is dried to the desired final moisture content, preferably around 3 or 4 to 6%.

After its final coating operation, whether a single coat or double coat, the dried paper is then usually passed through a suitable final machine calender stack indicated generally by the numeral 300 .where it is subjected to nip pressures of the order of 195 to 215 pounds per linear inch.

As stated above the metering rolls should be adjusted so as to give very accurate metering of the quantity of suspension passing the metering nip and traveling thence upon the surface of the roll to be carried around and brought into contact with the traveling web of paper at the nip of the application rolls 35-46. If less than the desired amount of mineral is carried to the nip, for any suitable length of time, even though the deficit be very small in quantity, the receptivity of the paper surface being therefore in excess of the quantity of mineral suspension applied to it, an unsatisfactory surface will be 28 secured since it will be non-uniform and even discontinuous, and also not adequately smooth. If this inadequate supply is continued for any length of time the rolls 35-36 tend to run completel y on the surfaces and this in turn tends to cause the rolls to be irregularly sticky with respect to the color and to thus make an uneven and irregular application of color upon the paper as it leavesthe nip of the rolls. In actual practies the metering rolls are accurately controlled so that somewhat in excess of the amount required to be applied to the paper will be on the surfaces of these rolls beyond the metering nip to be carried on into the nip against the paper. By properly coordinating the composition and characteristics of the mineral suspension. the receptivity and absorptivity of the paper, and the uniformity of spreading and distribution of the color in and upon the paper as it passes through the nip, 9. very, limited, lubricating quantity of the suspension will remain upon the surface of each roll as it leaves the nip; which quantity, when the various controlling conditions are properly coordinated, apparently becomes a substantially constant factor and provides that very slight excess which is carried into the nip and which, though very slight, is sufficient to prevent the rolls from running dry, or from becoming irregularly dry with the attendant difficulties described, When such operations are satisfactorily in progress the surfaces of the rolls 35 and 36 are wet or moist with this slight excess of color after the paper with its applied layer of color at the exit of the nip has moved away and out of contact therewith, a desirable and satisfactory operating condition being indicated where these rolls as they leave the nip are thus lubricated or moist on the surface.

Also, as stated, it is not necessary that effort be made to utilize the metering rolls 31-31 for applying a continuous and uniformly spread film of the metered color suspension across the faces of the rolls 35-35. In fact, it is unnecessary to even approach such a condition, and in satisfactory commercial operations referred to and with the formulas, meter pressures, etc. described the metered color upon the faces of the rolls 35-46 as it moves up to the nip and is brought into contact with the paper entering the ni is readily observed as being ridgy and of non-uniform depth. In fact, satisfactory results have been secured where the metered color being carried to the nip is discontinuous, being in ridges which are either completely or substantially unconnected by a thinner film of color. This may be indicated by lifting the roll and applying a sheet of paper to it as it approaches the nip whereby a discontinuous pattern may be trans ferred onto the paper. But for satisfactory operating conditions it has been found that the solids content, the consistency and the nip pressures for the suitable raw stock should be so controlled that at the nip where the color is applied to and spread upon the paper the ridges and irregularities and the general distribution shall be such that the color suspension will be flowed to blend and equalize uniformly across the paper web under such pressures. When a color is used of suitably controlled characteristics with respect to the paper to be of high fiowability after its application to the paper as it moves from the nip, additional fiowing' and equalizing occurs, even sufilcient with some colors to produce smoothness of finish despite obvious irregularities at the point of exit.

While the methods and forms of apparatus 1 29 herein describedconstitute preferred embodiments of'the invention. it is to be understood colortothe conditioning and applying rolls, subjecting the normally highly viscous or ing a nip-trough, means forsupplya coating color thereto to eiiect formation in said niptrough of a uniform andhomogeneous coating mass, said means comprising a plurality of spaced discharge nozzles connected to a source of coating color and located to discharge quantities of color directly into the nip-troughand means for reciprocating said nozzles longitudinally of said nip-trough with a predetermined stroke to provide for introduction of the coating color to said nip-trough to maintain a body of color of predetermined depth and in a substantially uni- .formly distributed manner.

2. In the manufacture of paper of the character described having a mineral finished surface adapted to receive printing impressions; the method which comprises passing a paper web between the traveling surfaces of color applying rolls, maintaining a substantial pressure of not less than about four pounds per linear inch across the application nip of said rolls; supplying a mineral and adhesive coating color comprising essentially coating pigment and an adhesive and a lubricating agent therefor and having solids content of not less than about 40-56%, and which coating color is of high thixotropy and is normally highly viscous or non-flowable and at 40 R. P. M. of a McMichael viscosimeter has a viscosity reading of approximately not more than 50 poises in a maintained quantity to be conditioned, subjecting said maintained color to high substantially non-flowable color to high shear working by the traveling surfaces at the nips of the conditioning and metering rolls .and color application rolls to eifect temporarily a large drop in viscosity to change the color into fluid and readily flowable condition, maintaining said condition for a limited operating time, metering said conditioned color between the traveling sur-' Y faces of said metering and conditioning rolls while u in S id rolls toward each other to pro vide metering surfaces separated from each other by said conditioned color under high pressure eiiective onsaid color of not less than 4 pounds per linear inch of roll length, said metering being accomplished in two successive high shear metering operations under said substantial pressure and said second metering operation being effective upon said metered color from the first metering operation while its metered condition is maintained, and applying said conditioned and metered coating color in said metered condition continuously to said traveling web of paper as the paper and metered quantity of color pass through the color application nip between said application rolls and controlled in quantity such that all the metered color will pass into the application nip, with the traveling pap r web, and subjecting the color to distribution pressure in the application nip to give a uniform blending and distribution of the color applied on the paper while said temporarily fluid condition persists in said coatshear working to cause large decreasein viscosity of said color to temporarily low viscosity and fluid condition, metering said colorwhile maintaining said temporary low viscosity condition across the surface of one of said applying rolls,

the amount of said color metered to said color applying roll being controlled to all, pass through the application nip with the traveling paper web and in limited excess of that to remain as a coat- .ing on the web, the pressure at the application nip being maintained substantial and such as to cause pressure distribution and blending of the metered color on the web, and causing adhesion separation of said excess color from the amount of color carried away from the application nip on the paper web, said separated excess adhered to the application roll and being carried by it away from the nip and admixed with the conditioned color prior to completion of the metering.

3. The method in the coating of a web of paper to produce a printing surface, through the utiliplying a maintained quantity of saidcoating ing color, to form a substantially smooth and uniformly distributed coating on said paper.

4. The method in the coating of a web of paper to produce a printing surface, through the utilization of coating means, comprising conditioning and meter rolls and application rolls, and a highly thixotropic suspension of coating color comprising mineral pigment and adhesive and of predetermined high solids content of not less than about 40 to 56% solids andwhich color normally is in highly viscous or substantially non-flowable condition, such that at 4.5 l't. P. M. of a Mc- Michael viscosimeter it has a viscosity reading of not less than about -135 poises and at 40 B. P. M. of the McMichael viscosimeter not more than about 16.5-50 poises, which comprises supplying a maintained quantity of said coating color to the coating conditioning and applying rolls, subjecting the normally highly viscous or substantially non-flowable color to high shear working by the traveling surfaces at the nips of the conditioning and metering rolls and color application rolls to effect temporarily a large drop in viscosity to change the color into fluid and readily flowable condition, maintaining said condition for a limited operating time, metering said conditioned color between the traveling surfaces of said metering and conditioning rolls while urging said rolls toward each other to provide metering surfaces separated from each other by said conditioned color under high pressure effective on said color of.not less than 4 pounds per linear inch of roll length, and applying said conditioned and metered coating color in said metered condition continuously to said traveling web of paper as the paper and metered quantity of color pass through the color application nip between said application rolls and controlled in quantity such that all the metered color will pass into the application nip with the travelingpapcr web, and subjecting the color to distribution presume in the application nip to give a uniform blending and 

